Fabricating integrated circuits is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconductor, typically silicon. The entire manufacturing process, from start to finish, takes six to eight weeks and is performed in highly specialized facilities referred to as fabrication plants. Fabrication plants require many expensive devices to function. Estimates put the cost of building a new fabrication plant over one billion U.S. dollars, with values as high as $3-4 billion not being uncommon. As a result, processing time in a fabrication plant is very valuable. Any time that a fabrication plant is not operating, for example for maintenance of a machine within the plant, is very undesirable.
So there is a need for all wafer processing steps to be extremely reliable with minimal maintenance required, and also for all processing steps to be made a quick as possible and to take a little space as possible.
As part of making processes reliable and in order to ensure that the circuits being produced operate properly, it is desirable to be able to test wafers for defects and faults at various stages of production. While optical inspection of surface features can be achieved rapidly and reliably, inspection of internal faults, such as voids, cracks and misalignments in deposited conductive elements (such as through silicon vias, copper pillars and bumps) is more difficult. Current methods for detecting these faults require taking a wafer out of the fabrication plant and testing using a focussed ion beam, scanning electron microscope or x-rays. However, as soon as a wafer is taken out of the clean environment of the fabrication plant it is effectively destroyed and can no longer be used.
It would be desirable to be able to accurately test semiconductor wafers for voids, cracks and misalignments in deposited conductive elements, in a more efficient and non-destructive manner. It would also be desirable to be able to test semiconductor wafers for voids, cracks and misalignments in deposited conductive elements quickly, in a manner that does not lead to significantly increased processing time for semiconductor wafers.